Justification of (3). When the discriminant of the quadratic equationa⁢s2+b⁢s+c=0asuperscripts2bsc0as^{2}\!+\!bs\!+\!c=0vanishes, the roots coincide to s=-b2⁢asb2as=-\frac{b}{2a}, and a⁢s2+b⁢s+c=a⁢(s+b2⁢a)2asuperscripts2bscasuperscriptsb2a2as^{2}\!+\!bs\!+\!c=a(s+\frac{b}{2a})^{2}. Therefore (2) reads